Multiple section irrigation sprinkler systems such as employed for golf courses, highway green belts, and farms require accurate and reliable control of the sequencing and operation of each of the multiple sections to avoid damage to vegetation. Many golf courses, for example, employ a centrally located microprocessor or computer to control electrically actuated valve assemblies for the sequencing and operation of the sprinklers in each section of the multiple section irrigation sprinkler system.
An electrically controlled irrigation sprinkler system can require many miles of underground wire that is frequently damaged by gophers, tree roots, or the like, as well as by lightning strikes during electrical storms. In many geographical areas, the frequency and severity of electrical storms limit the use of electrically controlled irrigation sprinkler systems.
Golf courses in these areas of frequent electrical storms often employ a system of hydraulically actuated valve assemblies wherein each valve assembly is connected by a network of water tubes to a central station. Computer controlled switches control the pressure in the individual water tubes as required by the programmed irrigation cycle to control each hydraulically actuated valve assembly to turn each section of the irrigation sprinkler system on and off selectively. These hydraulically operated systems are relatively immune to the effects of electrical storms, but are particularly susceptible to the damage caused by gophers and tree roots.
In an attempt to overcome such problems, pressure actuated control systems using pressure changes in the main water supply lines to control the sequencing and operation of each section of multiple section irrigation sprinkler system have been proposed, and would overcome most or all of the problems encountered with the aforementioned electric and hydraulic control systems. For example, irrigation sprinkler systems and control techniques and components are disclosed in U.S. Pat. No. 3,747,620, IRRIGATION SPRINKLER SYSTEM CONTROL EMPLOYING PILOT OPERATED, PRESSURE ACTUATED AND SEQUENCED VALVE ASSEMBLIES and in U.S. Pat. No. 3,797,740, FLUID DISTRIBUTION SYSTEM OPERATED BY PRESSURE SIGNAL. The foregoing patents are incorporated herein by reference.
However, such pressure actuated control systems introduce new unique system control problems. Such systems and techniques apparently were previously employed on several golf courses. Such pressure actuated control systems employ pilot operated, pressure actuated valve assemblies similar to the one described in U.S. Pat. No. 3,747,620. The pressure actuated valve assemblies included internal rotary cams each having 39 index positions. Additionally, each pressure actuated valve assembly included adjustable devices to select the specific cam index position for activating an associated sprinkler. The pressure actuated valve assembly also included an internal mechanism for causing the rotary cam to rotate one index position each time the water supply pressure was reduced from 60 psi to 40 psi and then was increased back to 60 psi. Thus, a series of controlled changes in the water supply pressure provided the mechanism for the complete control of the sequencing and the operation of a multiple section irrigation sprinkler system to activate and deactivate selectively the sprinklers controlled thereby.
To initiate a series of sequencing and operating cycles in such a pressure controlled irrigation sprinkler system, the central control system first reduced the water supply pressure to 12 psi. The reduced water pressure of 12 psi caused each of the pressure actuated valve assemblies to reset an internal rotary cam to the starting position. The control system next raised the water supply pressure to 90 psi to "initialize" or prepare all of the pressure actuated valve assemblies for the start of the sequencing and operating cycles. After the application of the initial 90 psi pressure, the rotary cam in each pressure actuated valve assembly would index one position each time the water supply pressure was lowered below 40 psi and then increased to over 60 psi. Each time the water supply pressure was increased to over 80 psi after an indexing operation, all of the pressure actuated valve assemblies and associated sprinklers selected by the last selected rotary cam position would turn on, while all of the remaining pressure actuated valve assemblies and associated sprinklers would remain deactivated.
Reduction of the water supply pressure from 90 psi to under 40 psi in a reasonable length of time required the operation of a pressure regulating valve to reduce the applied system pressure and the opening of a "dump valve" to relieve the pressure in the water supply line. Then, the control system operated the pressure regulating valve to increase the applied system pressure and close the dump valve to return the system water supply pressure back to 90 psi to activate the next set of sprinklers.
The opening and closing of the pressure regulating valve and the dump valve did randomly result in the effect known as "water hammer," especially in irrigation sprinkler systems that had been in long-term service. The term water hammer is defined to describe the series of sudden pressure changes caused by abrupt changes in the rate of flow of a large mass of water in a closed hydraulic system.
The water hammer effect did randomly occur when either the pressure regulating valve was operated or the dump valve was opened and closed. The water hammer effect caused the water pressure in the system to rise rapidly and unpredictably above 60 psi and then fall below 40 psi several times during a single cycle programmed to index the rotary cam only one index position in the pressure actuated valve assemblies. Thus, when the water supply pressure was lowered below 40 psi and then increased to over 60 psi, as a result of the water hammer effect, the rotary cams in the pressure actuated valve assemblies were uncontrollably indexed more than the desired single position commanded by the program in the control system. The rotary cams oftentimes were indexed as much as three positions when a change of only one index position was commanded by the control system. As a result, the operation of several sections of the multiple section irrigation sprinkler system were skipped during a regularly scheduled irrigation cycle, resulting in dead or dying grass and costly damage to the golf course.
As a result of the foregoing problems associated with the pressure actuated control system, they are no longer popular, and currently the electrically controlled irrigation systems are preferred.
Therefore, it would be highly desirable to have a new and improved pressure activated control system, which can function reliably and accurately, and eliminate undesirable malfunctioning as experienced in prior known pressure activated irrigation control systems.